Furnace heating element



Patented i 13, 1939 UNITED" STATES PATENT OFFICE FURNACE HEATING ELEMENTLe Roy L. Wyman, Schenectady, N. Y., assignor to General ElectricCompany, a corporation of New York No Drawing. Application April 30,1937. Serial No. 139,938

11 Claims. (Cl. 75-123) tric furnaces which employ reducing atmospheres:1 containing carbon monoxide gas.

Prior to the present invention it has been customary to employ alloyfurnace heater wires or ribbons containing about 80% nickel and 20%chromium. Alloys of this composition have a cold resistance of about 105microhms per cubic centimeter and at operating temperatures theresistance increase is about 5%. However, when operating in furnaceatmosphere containing carbon monoxide and at temperatures in theneighborhood of about 1000 C. this alloy or any alloy containingchromium or aluminum-gradually disintegrates and ultimately failscompletely due to corrosion of the chromium or aluminum. The corrosionis quite rapid at a furnace temperature of about 1000 C. and more slowlyat lower temperatures.

It is an object of the present invention to pro vide an alloy suitablefor use in a furnace as a heater element or other device which resistscorrosion in furnace atmospheres containing carbon monoxide and whichhas desirable electrical and physical characteristics. Other objectswill appear herinafter.

In carrying out my invention I employ an alloy consisting of one or moreof the metals of the iron group and one or more of the elements of thegroup consisting of molybdenum and tungsten. Preferably I employ analloy consisting principally of nickel.

oxidation at high temperatures in an atmosphere containing carbonmonoxide, it does not have the requisite strength or electricalcharacteristics for use as a furnace heater-element. The alloy which Iprefer to employ as a heater element contains -l0 about 80% nickel and20% molybdenum. An alloy of this composition has substantially the samestrength at operating furnace temperatures as the 80% nickel, 20%chromium alloy. It also has a cold resistance of about 105 microhms percubed centimeter and the resistance increase at operating furnacetemperatures in the neighborhood of 1150 C. is about 10%. However, thenickel-molybdenum alloy is substantially unaffected by reducing furnaceatmospheres, and

particularly those containing carbon monoxide, at any temperature. It isalso easy to work and has a very long life as compared to heaterelements containing chromium.

The nickel-molybdenum alloy may contain from about 5 to 40% molybdenum.Those alloys While pure nickel resists which contain the lowerquantities of molybdenum change considerably in resistance in going fromthe cold state to the operating furnacetemperature. Also, those alloyscontaining the higher percentages of molybdenum have a tendency towardbrittleness. I prefer therefore to employ nickel-molybdenum alloyscontaining more than 12% but not more than 40% molybdenum.

If desired, tungsten may be substituted for the molybdenum in whole orin part. If an alloy consisting of nickel and tungsten is employed, the

tungsten content of the alloy may vary from about 2 to 45% of the totalcontent of the alloy and preferably is somewhat higher than the quantityof molybdenum which may be employed with nickel.

If desired I may add molybdenum or tungsten, or both, to one or more ofthe elements iron, nickel and cobalt. Alloys consisting for. example ofabout nickel, 20% molybdenum and 15% iron; and 65% nickel, 12%molybdenum and 23% iron or corresponding nickel-iron-tungsten alloysgive satisfactory results as to strength, electrical characteristics,and resistance to oxidation in atmospheres containing carbon monoxidegas. In fabricating the alloys containing iron and molybdenum, forgingis facilitated if a small quantity of manganese, i. e. about .5%, isadded to the alloy and if the forging is carried out at a temperature ofabout 1250 C.

While the above alloys are particularly adapted for use as heaterelements in furnaces employing reducing atmospheres containing carbonmonoxide gas their use is not limited to such furnace atmospheres or toheater elements. The alloys, if desired, may be employed to advantage inthe construction of furnace equipment such as rolls, brackets, or othersupporting means, hearths, tracks, conveyor links and the like.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An alloy heater element consisting of metal a of the iron group andmetal from the group consisting of tungsten and molybdenum, the metalfrom said group consisting of tungsten and molybdenum comprising about2% to 45% by weight of said alloy. I

2. An alloy heater element consisting substantially of nickel and metalfrom the group consisting of molybdenum and tungsten, said metal fromsaid group comprising about 12 to 40% of said alloy.

3. An alloy furnace heater element consisting principally of nickel, theremainder of the alloy consisting of about 5% to 40% molybdenum.

2 areasaa 4. An alloy furnace heater element containing about 80% nickeland 20% molybdenum.

5. An alloy furnace heater element subject to furnace temperatures andto a reducing furnace g atmosphere containing carbon monoxide, saidalloy containing about 65% nickel the remainder of the alloy consistingof about 13% to 23% iron and about 12% to 20% molybdenum.

6. An alloy comprising a portion of the equiplo ment of a furnace, saidalloy being subject to the temperature and atmosphere of said furnace,said alloy consisting of metal of the iron group and metal from thegroup consisting of tungsten and molybdenum, said metal from the groupconsisting of tungsten and molybdenum comprising about 2% to 45% byweight of said alloy.

7. In a furnace attachment or structure, an alloy subject to elevatedfurnace temperatures and to a furnace atmosphere containing carbon mongooxide said alloy consisting principally of nickel but containing about12 to 40% of metal from the group consisting of tungsten and molybdenum.

8. An alloy comprising a portion of the equipg5 ment of a furnace andsubject to elevated temperatures and to a furnace atmosphere containingcarbon monoxide, said alloy containing about 80% nickel and 20%molybdenum.

9. In combination, a furnace employing a reducing atmosphere containingcarbon monoxide 5 gas and an alloy heater element therein, said alloyconsisting of metal of the iron group and metal from the groupconsisting of tungsten and molybdenum, the metal from said latter groupcomprising 2% to 45% by weight of said alloy.

10. An alloy furnace attachment or structure subject to elevated furnacetemperatures and to a furnace atmosphere containing carbon monoxide,said alloy consisting of about 65% nickel, 12% to 20% molybdenum, and to23% iron. 15

11. An alloy furnace attachment or structure subject to elevated furnacetemperatures and to a furnace atmosphere containing carbon monoxide,said alloy consisting of metal from the iron group and metal from thegroup consisting of tungsten and molybdenum, the metal from the lattergroup comprising more than 12% but not more than of said alloy.

LE ROY L. WYMAN. g5

